The present invention relates to a piston pump which is adapted for use in inflating a balloon, a yo-yo balloon, a bag, etc.
As for the means for inflating a balloon, a yo-yo balloon, a bag, etc. by introducing air or water into them, a simplified piston pump is known wherein a piston inserted into a cylinder is reciprocatively moved several times depending on the size of the balloon, etc. so as to inhale air or water into the cylinder and exhale it out of the cylinder through the nozzle thereof. In order to enable the piston of the pump to be reciprocatively moved safely and effectively, it is required that the piston is prevented from slipping out of the cylinder and that the shaft of piston is prevented from being decentered. If the piston slips out of the cylinder during the pumping operation of the pump, the operation of the piston pump is caused to interrupt, thus wasting the time for the inflation operation of the balloon, etc. On the other hand, if the shaft of piston is decentered on the occasion of reciprocative movement thereof, not only the reciprocative movement of the piston becomes difficult, but also a gap is caused to generate between the piston and the cylinder, thus deteriorating the function of the piston pump.
In most of the conventional piston pumps, the prevention of slipping-out of piston and the decentering of the piston shaft are effected by making use of a bearing cap. Namely, the bearing cap is a cap which fits on the cylinder and is provided at the center thereof with a through-hole for allowing the piston shaft to pass through, thus functioning as a bearing for the piston shaft. When a piston is attached to the piston shaft, the piston is caused to impinge against this bearing cap, thereby preventing the piston from slipping out of the cylinder. However, since the bearing cap is employed, the piston or operating grip is required to be attached to the piston shaft after the piston shaft has been inserted into the bearing cap. Therefore, the piston, piston shaft and operating grip are prepared separately, thus increasing the number of parts and also taking a lot of time for the assembling of them, resulting in an increase in manufacturing cost.
For example, Japanese Utility Model Unexamined Publication S56-155,862, Japanese Patent Unexamined Publication H7-310,649, and U.S. Pat. No. 5,655,890 set forth respectively a simplified piston pump of this kind.
Namely, Japanese Utility Model Unexamined Publication S56-155,862 discloses a piston pump which is featured in that the cylinder is made transparent, thereby making it possible to visually recognize the quantity of water introduced into the cylinder. Japanese Patent Unexamined Publication H7-310,649 discloses a piston pump which is featured in that the piston is molded from plastic material, thereby improving the sealing property as well as the smooth movement thereof relative to the cylinder. U.S. Pat. No. 5,655,890 discloses a piston pump which is featured in that both piston and cylinder are respectively provided with a one-way valve. However, since all of these known piston pumps utilize a bearing cap, they would accompany the same problem that the number of parts is increased and a lot of time is required for the assembling of them, resulting in an increase in manufacturing cost.
There is also known a simplified piston pump which has no bearing cap among the simplified piston pumps which are now available in the market. According to this piston pump, the piston shaft is of a cylindrical configuration, so that the outer peripheral surface of piston shaft is continuously contacted with the inner surface of the cylinder, thereby preventing the piston shaft from being decentered. This piston pump however is accompanied with a problem that since the cylindrical piston shaft is always contacted with the inner surface of the cylinder, it is impossible to provide the piston pump with means for allowing it to be contacted with the piston so as to prevent the piston from being slipped out.
Therefore, it is an object of the present invention to provide a simplified piston pump which employs no bearing cap, nevertheless, is capable of preventing the piston from slipping out of the cylinder and also capable of preventing the shaft of piston from being decentered. It is now made possible according to this piston pump to reduce the number of parts, to simplify the manufacturing process and to greatly save the manufacturing cost thereof.
The bearing cap according to the conventional simplified piston pump functions in two ways, i.e. for preventing the piston from slipping out of the cylinder and for preventing the shaft of piston from being decentered.
Therefore, the present inventors have made an extensive study for developing a simplified piston pump which has no bearing cap, but nevertheless, is capable of exhibiting the functions that the conventional bearing cap could provide.
First of all, it has been made possible by the present inventors to prevent the piston from slipping out by forming a protruded portion on the inner wall of proximal end portion of the cylinder. Due to the existence of this protruded portion, the piston is caused to impinge against this protruded portion even if it is tried to pull and disengage the piston from the cylinder, thereby making it possible to prevent the piston from inadvertently slipping out.
Then, it has been studied by the present inventors to realize the prevention of the decentering of piston shaft without necessitating the employment of the bearing cap. According to the aforementioned piston pump having no bearing cap, the piston shaft thereof is made cylindrical so as to make it entirely contact with the inner surface of the cylinder. It is certainly possible in this case to prevent the decentering of the piston shaft, but it is impossible to form a protrusion on the inner surface of the cylinder as proposed by the present invention. Under the circumstances, it has been intensively studied to find out a structure which enables the piston shaft to reciprocatively move even if the protrusion for preventing the slipping-out of piston is formed on the inner surface of the cylinder. As a result, it has been resulted in the invention of a piston shaft having a structure wherein the outer surface of the piston shaft is contacted with the inner surface of the cylinder so as to prevent the decentering of the piston shaft and wherein a groove is formed thereon so as to ensure the reciprocative movement of the piston. More specifically, by constructing the piston shaft in such a manner that irrespective of where the piston shaft is located within the reciprocating region thereof, the outer surface of the piston shaft is partially contacted with the inner surface of the cylinder so as to prevent the axial center of the piston shaft from being dislocated, it becomes possible to prevent the decentering of the piston shaft. For example, if the piston shaft is made into a triangular columnar configuration which is designed to be contacted with the inner surface of the cylinder, three ridge lines corresponding to the peaks of the triangular configuration are always caused to contact with the inner surface of the cylinder irrespective of the location of the piston shaft, thereby preventing the axial center of the piston shaft from being dislocated and hence preventing the decentering of the piston shaft.
Further, by forming the groove of the piston shaft in such a manner that it extends linearly and parallel with the reciprocative moving direction of the piston shaft, the protrusion formed on the inner surface of the cylinder for the prevention of the slipping-out of the piston is allowed to pass through the groove of the piston shaft. Therefore, even if the protrusion is formed on the inner surface of the cylinder, the piston is enabled to reciprocatively move inside the cylinder. It is now possible, through the employment of the piston shaft of the present invention, to prevent the decentering of the piston shaft and to form a protrusion on the inner surface of the cylinder for the prevention of the slipping-out of the piston. Namely, by the provision of the protrusion formed on the inner surface of the cylinder and also by the employment of a piston shaft having the aforementioned decentering-preventive function and groove, the piston can be prevented from slipping out and at the same time, the piston shaft can be prevented from being decentered without necessitating the employment of the bearing cap.
The disuse of bearing cap brings about a positive effect that, as explained hereinafter, the piston, the piston shaft and the operating grip can be integrally molded.
As for the method of forming the aforementioned protrusion on the cylinder, it is possible to employ a method wherein a protrusion member prepared separately is attached to the cylinder by making use of an adhesive, etc., or to employ a method wherein a hole or holes are formed in the cylinder in advance and then, a protrusion member is fitted in the hole, both methods falling within the scope of the present invention.
Another positive effect to be derived from the disuse of bearing cap according to the present invention is the possibility of integrally molding the protrusion and the cylinder. Namely, a portion to be formed into the protrusion is molded integral with the cylinder in such a manner that this portion can be subsequently bent. Accordingly, before the piston is inserted into the cylinder, this portion to be formed into the protrusion is not protruded into the interior of the cylinder, but after the piston is inserted into the cylinder, this portion to be formed into the protrusion is bent inward so as to allow this portion to protrude into the cylinder. It is possible with this method to realize the prevention of slipping-out of the piston and the integral molding of the protrusion and the cylinder, thereby making it possible to greatly reduce the number of parts as well as the number of molds, and to simplify the assembling process, thus saving the manufacturing cost.
According to the present invention, there are provided:
(1) A simplified piston pump which is enabled to function through a reciprocative movement of piston, said piston pump comprising a cylinder having at least one protrusion formed on the inner surface of a proximal end portion of said cylinder for preventing the piston from slipping out, and a piston shaft having a structure wherein the outer surface of the piston shaft is contacted with the inner surface of the cylinder so as to prevent the decentering of the piston shaft and wherein a groove is formed thereon so as to ensure the reciprocative movement of the piston.
(2) The simplified piston pump as set forth in above item (1) wherein said at least one protrusion is formed integral with a main body of said cylinder.
(3) The simplified piston pump as set forth in above item (1) wherein said at least one protrusion is fastened to a main body of said cylinder.
(4) The simplified piston pump as set forth in above item (1), (2) or (3) wherein said piston, said piston shaft and an operating grip are formed integral with each other.
In this specification, the expression of: xe2x80x9ca proximal end portion of cylinderxe2x80x9d means a portion of the cylinder which is located closer to the operating grip and is not intended to limit the location thereof to a specific point. Namely, when the protrusion for preventing the slipping-out or disengagement of piston is formed closer to the operating grip, the stroke of the piston can be made longer proportionally.